actually if I try to send a wrong query http://localhost:1080/api/v1/?register=CUVc to rest api v2 on version 8.4, it tries v1 I guess:
2017-09-26 09:12:47 AD F3Get fieldname not found
2017-09-26 09:12:47 AD dump of call stack
2017-09-26 09:12:47 AD call stack entry: amainhal/WebDataAPI.hal: DOEXPORT_CUVC
2017-09-26 09:12:47 AD call stack entry: amainhal/WebDataAPI.hal: WEBDATAAPI

and crashes single user server.
This http://localhost:1080/api/lets_crash_this_server query also crashes the single user server 8.4 2017-09-14 (build 84190303)

I have already reported the issue.